I don't even think you need that resistor. I never used it. Tried it once, but didn't hear any improvement, only the signature of a resistor. It was Mills 5W.

I used to think like that 'till I build this surround amp. When I connected the speaker cables (almost 10 meters long) one of the amps went into oscilation.At first I didn't notice, It was hot,and the sound was edgy, if you know what I mean.
So I hoked up the osciloscope and I clearly saw that the oscilation started when the cable was connected. If I put the resistor-even a .1 value, this oscilation do not start.

You might try to post a wanted ad, as many people took part in the Mills group buy and I don't think all of them are using the resistors , especially when the fame went on that Aleph X sounds best with higher PS voltage

Those were Mills wirewounds, 0.22ohm, 5W, perfect choice for a GC. I bought 100 of them, but I have a feeling I will use all of them

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The price is $3 at partsconnexion. We were buying them directly from manufacturer at $1 a pc (1000 qty.)

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“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

>You certainly agree, that they (Rikens, Caddocks or generic type) provide different sound in some locations.<

Rikens and Caddocks don't even measure alike. But it does seem that there are sonic differences between nominally similar-structure resistors - Vishays vs. Alpha being one such case.

OTOH, the properties desired of a resistor for one location may be rather different from those in another location. Besides, some locations may simply not be very sensitive.

>I'm not trying to promote one brand over the other, but simply indicate, that experimentation is worth the trouble.<

Resistor experimentation is certainly easy enough to do. But it can be pricey, as you have undoubtedly noticed. And if you decide on a resistor that happens to be fairly expensive, you will pay a significant price penalty for each and every amplifier that you build,

>Since there is not much opportunity to improve the schematic design.<

If the amplification mode is non-inverting, you could bootstrap the entire power opamp. The bootstrapping could either track the output, or it could be compensated back to the input, similar to the methods outlined in Analog Device's AN232 by Walter Jung. Other interesting ideas would be to use digital power amps as the bootstrapping devices. Run a virtual ground. Maybe regulate everything - which could be linear or switching. Or perhaps low-loss synchronous rectification. No need to be shy

>and PCB is not required here<

PCB or no PCB, some type of physical structure will be required, and here it definitely pays to think, calculate and experiment. I am currently designing a partially PCB, partially P2P structure for one of my products, and I am up to revision #24. Based on my experience over the years, experimenting with the physical structures (including pcb) has much more potential to benefit the sound than swapping resistors (assuming that each location already has a resistor that has suitable properties for how it will be used). Experimentation with board and structure design requires time, effort, and money, but once the design has been finalized, you don't have to pay a price penalty on each and every amplifier that you produce. Unlike premium-grade resistors.

Mind you, I am not against using high-quality components. But what I see is that many DIY'ers jump to expensive components without doing the basics - which is to put as much thought, study and care as possible into their schematics and structures. As I have said before, high-quality components should be regarded as the icing on the cake of thorough and careful design - they should not be considered a substitute for incomplete or inept design.

Do you have any views w.r.t. the ferrous / non-ferrous state of components / leads.

I've used for years the basic Beyschlag MRS25 metal films - they are cheap, low noise and sound acceptable.

The Vishay / Dale RN60's I've been kindly sent by a partner are a lot better sounding though, and this is in a PSU regulator application, not a 'direct' signal path app.

There are a number of obvious differences: -

a) The RN60's ar more conservatively rated w.r.t. Pd ratings.

b) They are physically larger.

c) They are of a non-magnetic construction.

I'm utterly convinced of the sonic benefits, but cannot easily pin the effect to a single cause - I've found copper-leaded caps to sound better too, but how much of this is due to the fact that these devices are aimed at audio, generally, and have other characterisitics that are better?

The Welwyn RC55's are an interesting example I should try - these have steel endcaps but are reported to sound good.

I for one would be vry grateful for your input or ideas, primarily because the options open to me at the moment are all expensive, and I'm a cheapskate

Finally I agree that these are 'icing on the cake' and that other issues are often more important. Most would be better placing their efforts elsewhere for big improvements.

I was specifically talking about GC amp and the parts selection for inverting mode of operation. Simplicity was a key to the expected performance and I was not really tempted to complicate matters by using bootstraping or regulated supplies. Although I didn't try regulators, my feeling is they would not bring any improvement.

This circuit is very sensitive to any changes and because it uses only 2 extra parts (beside IC), any differences caused by the resistors are immeditely obvious.

Although the circuit is very simple, I spend countless hours on experimenting and tweaking until the performance became satisfactory. For instance, I noticed that paralleling PS caps is not good and single cap sounds better. Adding bypass caps (so popular with both DIY and established companies) is not good either, as although it may seem nicer sounding in the beginning, takes away natural integrity from the sound.

I was initially quite satisfied with Riken in feedback loop (which was already improvement over Holco), but initial response from people testing amps, was lack of depth in the soundstage. I bought Caddock resistors long time ago, but didn't really have desire to try them out (if it works, why bother with different parts, was my partner's suggestion). Working on next project, the monoblocks, I put the Caddocks in a feedback location and to my suprise, they sounded just right, more liquid and dimentional than Rikens. Swapping Kimber umbilical cord to Cardas wire improved things even further.

So as you see, I'm not that crazy about exotic components (I'm not even taking plastic jackets off the caps) and using them as a cure for everything. But, if I see that a certain part makes a big difference, I just can't dismiss it. As I said earlier, my amp is using only 2 resistors. Comparing that to an average circuit, containing approx. 20 resistors, I think I can allow myself the luxury to pay $6 for my 2 pieces

Originally posted by jcarr
If you have exhausted all of your other possibilities, maybe.

Maybe you could tell me, is there anything here, that can be further improved structurally?
I'm a firm believer that structure design of any audio unit has big influence on final performance, sometimes even bigger than the resistors, indeed
After all, my actual background is in aircraft structures, not electronics, so it should be understandable that I prefer to play with parts and not schematics.

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“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

Peter: If your approach works for you, and if you are happy and confident with the results, there is no need for you to be concerned with my opinion, or anyone else's. It's your design, right?

>Maybe you could tell me, is there anything here, that can be further improved structurally?<

With your background, I am sure that you are just as capable as I am at designing physical structures - possibly more so. FWIW, I do a fair amount of pcb layout and P2P design work using a mechanical CAD program (VectorWorks) in addition to a PCB program (Protel 98).

>it should be understandable that I prefer to play with parts and not schematics.<

Ah, but studying new things and gaining new abilities is always a joy. If you get into it, electrical schematics and structures are just as much fun as mechanical designs and structures.

Mind you, I am not against using high-quality components. But what I see is that many DIY'ers jump to expensive components without doing the basics - which is to put as much thought, study and care as possible into their schematics and structures. As I have said before, high-quality components should be regarded as the icing on the cake of thorough and careful design - they should not be considered a substitute for incomplete or inept design.

Couldn't agree more. I see terribly built devices with the most expensive components too often.

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It's only audio. Member of the non modular PCB design committee

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“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC